check initializer to be zero in .bss-like sections

check initializer to be zero in .bss-like sections

Just like gas, which has recently learned to reject such initializers,
gcc shouldn't accept such either.

gcc/
2016-07-01  Jan Beulich  <jbeulich@suse.com>

	* varasm.c (get_variable_section): Validate initializer in
	named .bss-like sections.

gcc/testsuite/
2016-07-01  Jan Beulich  <jbeulich@suse.com>

	* gcc.dg/bss.c: New.

From-SVN: r237913